644805665 has 16 divisors (see below), whose sum is σ = 936323712. Its totient is φ = 416143104.

The previous prime is 644805613. The next prime is 644805709. The reversal of 644805665 is 566508446.

644805665 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a cyclic number.

It is not a de Polignac number, because 644805665 - 2⁸ = 644805409 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 541259 + ... + 542448.

It is an arithmetic number, because the mean of its divisors is an integer number (58520232).

Almost surely, 2^644805665 is an apocalyptic number.

It is an amenable number.

644805665 is a deficient number, since it is larger than the sum of its proper divisors (291518047).

644805665 is a wasteful number, since it uses less digits than its factorization.

644805665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1083736.

The product of its (nonzero) digits is 691200, while the sum is 44.

The square root of 644805665 is about 25393.0239435952. The cubic root of 644805665 is about 863.9254769864.

The spelling of 644805665 in words is "six hundred forty-four million, eight hundred five thousand, six hundred sixty-five".